completion-auto-helpcompletion-auto-help is a variable defined in `
minibuffer.el'. Its value is
tDocumentation: Non-nil means automatically provide help for invalid completion input. If the value is t the *Completion* buffer is displayed whenever completion is requested but cannot be done. If the value is `lazy', the *Completions* buffer is only displayed after the second failed attempt to complete. You can customize this variable.